The present invention relates to beams for supporting planar elements such as plates or panels and capable, in particular, of supporting the sheets of the fluidtight inner covering of a de-activation pool of a nuclear station.
Nuclear station pools or de-activation pools, are adapted to store substances irradiated after a stay in the reactor and thus permit tne de-activation over a period of time of the substances within a large volume of water which serves to absorb the radiations emitted by said substances so that these radiations are not freely propagated in the atmosphere.
Bearing in mind safety requirements, these pools must be perfectly fluidtight so as to avoid any escape of contaminated water. For this purpose, the de-activation pools comprise a fluidtight inner covering formed by sheets, for example of stainless steel, which are joined to each other by their edges by weld beads. In the region of the latter, the sheets are fixed to a structure formed by beams incorporated in the inner part of the corresponding wall of the pool, which is usually made from concrete, this structure thus supporting said sheets of the inner covering.
The distinction between an outer part and an inner part in respect of each wall results from the manner of constructing the latter which is carried out in two stages, the first stage consisting in making said outer part of the walls.
In this respect, such beams each comprise a flat bearing surface adapted to support the sheets and are connected to the outer part of the corresponding wall of the pool by a plurality of lugs which ensure their fastening to this outer part prior to their embedding in the concrete of the corresponding inner part. These lugs not only ensure the fastening of the beam but also serve to adjust its spacing from the surface of the outer part of the respective wall so as to compensate for unevennesses thereof.
A first type of beam is thus known which comprises a corner iron whose cross-section is substantially L-shaped, one bearing surface for the sheets, whereas the other flange cooperates with the fixing lugs. However, after the filling of the inner part of the walls by concrete, there is no longer any space capable of receiving a device for radiographing the weld beads so as to check their state.
Further, in the event of leakage in the region of said weld beads, the leakage is caused to infiltrate in an uncontrollable manner in the concrete if such a structure does not provide means for draining possible leakages.
In a second type of known beams, the latter each comprise a cross-section in the shape of a U on the edge of the wings of which is welded a flat strip of sheet which forms with said U-section a channel having a closed cross-section and defines a flat bearing surface for the sheets of the inner covering of a pool.
This type of beam provides an improvement in that a channel is formed for the radiography of the welds which is not liable to be obturated when pouring the concrete. However, no solution is provided for the problem relating to the draining of possible leakages.
Thus, in a third type of beam, the latter has a structure similar to those of the second type described before and is provided on its bearing surface with localized openings adapted to receive the liquid coming from leakages in the region of the weld beads. However, it has been found that the localized openings provided in the strip of sheet metal do not provide a very effective draining of the leakage liquid.